Sample size calculation The VISA-A has been suggested to be valid and reliable and is therefore strongly recommended for use when researching and treating Achilles tendon pain (Robinson 2001; Brukner & Khan 2007). Thus it will be used as the principle outcome measure of this investigation. Previous research suggests a delta of 10 points with a standard deviation of 12 when comparing eccentric exercise to a wait and see approach (Rompe et al 2008) giving a large effect size of 0.83. With a power of 0.80, an alpha level of 0.05, and using methods outlined by Fleiss (1986) it is calculated that 23 participants are required for each group of this trial. All studies in this area assign an additional 10% to the calculated sample size to account for loss to follow-up (Rompe et al 2007). This appears to be adequate for the proposed population and setting as no studies have failed to recruit the required number to ensure adequate power. Therefore a total of 26 patients will be required for each arm of this trial.